Skeletal Structures • One of the most useful skills in organic chemistry is the ability to write and understand skeletal structures . Let’s take a look at some skeletal structures for several alkanes: heptane 2,2-dimethylpentane cyclooctane tert-butylcyclohexane • For each of the following skeletal structures, count the number of carbon and hydrogen atoms in the structure, and provide a systematic name for the alkane: Reading : Section 2.5 Chemistry S-20ab Week 1 20

Functional Groups • One way to bring some order to the vast diversity of organic molecules is by classifying them based on the functional groups they contain. A functional group is a group of atoms bonded together in a particular way. Molecules that contain the same functional group tend to react in similar ways. Here are examples of some common functional groups: Carboxylic Acid Alcohol Alkene Alkyl Halide • In what other ways do functional groups play a role in classifying molecules? Reading : Section 2.9 Chemistry S-20ab Week 1 21

This preview
has intentionally blurred sections.
Sign up to view the full version.

Functional Groups, Skeletal Structures, and Organic Reactivity • One of the properties of alkanes is that they are generally not very reactive; conversely, any portion of a molecule that is not an alkane is likely to be reactive. How do skeletal structures help us to understand organic reactivity? • Here is the skeletal structure of palytoxin , one of the most poisonous compounds known. It is isolated from marine coral. Palytoxin was synthesized in 1994 by a group of researchers led by Professor Yoshito Kishi here at Harvard. It is probably the most complicated organic molecule that has ever been synthesized. Do you recognize any functional groups in palytoxin? Can you find any portions of the structure of palytoxin that will be unreactive ? Chemistry S-20ab Week 1 22

Molecular Orbitals: H 2 and He 2 • We originally showed that the overlap of atomic orbitals forms a single covalent bond. However, the mathematics of quantum mechanics requires that the number of orbitals must be conserved. Thus: when two orbitals are combined, two new combinations must result. How does this work in forming H 2 ? • This molecular orbital treatment can explain why H 2 exists but He 2 does not. We can define the bond order of a species as: Bond order = 1 2 (electrons in bonding orbitals – electrons in antibonding orbitals) Reading : Section 1.8 Chemistry S-20ab Week 1 23

This preview
has intentionally blurred sections.
Sign up to view the full version.